Cracking pattern of indented ice sheet bending failures

Ice sheet bending failures have been investigated extensively for ice loads on conical offshore structures and icebreakers in arctic regions. Most previous theoretical studies focus on bending failures of semi-infinite level ice, ice wedges, or finite-sized rectangular ice floes. For indented ice sheet bending failures, Nevel (1992) and Lau (2004) developed analytical ice load models by assuming a radial-before-circumferential cracking pattern. Recently, real-time simulations of ice-structure interactions are gaining increasing traction due to their great application potential. The analytical or semi-analytical models implemented into the real-time simulator significantly influence the accuracy of real-time simulations. Against this backdrop, the cracking pattern assumption needs to be more critically examined, and the criterion for cracking pattern determinations is in demand for utilizing different models for different cracking patterns in real-time simulations. Motivated by this need, the current paper establishes the cracking pattern determination criterion for indented ice sheet bending failures, based on the theory of plates on elastic foundations and normalized formulae. It is found that large indentation lengths and radii of structure waterline curvature induce a circumferential-before-radial cracking pattern. Conversely, small indentation lengths and radii of structure waterline curvature result in a radial-before-circumferential cracking pattern.

Stress State of 3D-Printed Plastic Dies at Thin-Sheet Aluminum Bending

The paper deals with the problems and prospects of forming thin-sheet blanks, using ABS plastic dies, made by 3D printing. This technology combines the positive properties of plastic material and 3D-printing. The mechanical characteristics of the plastic were determined experimentally. On the basis of computer modeling, the dependence between the angle of bending the blank and the stresses arising in the dies is established. As a result of computer simulation and physical experiment, the value of the maximum thickness 0.5 mm for the aluminum 3003 blank is obtained. In this case, there is no plastic deformation of the plastic tool. The use of plastic dies does not require lubrication. The technology of sheet bending, using a plastic tool, can be implemented with the greatest efficiency in single and small-scale production.

Invisible mechanical lap joints for metal–polymer laminates

Joining by compression of metallic inserts has been recently developed by the authors to create invisible lap joints between metal and polymer laminates. This paper revisits the process with the objective of proposing a new type of bi-material (polymer–metal) cylindrical insert for lightweight construction applications that is capable of ensuring complete filling of the joint at the end of stroke without increasing the forming force and the risk of sheet bending. The presentation is built upon a combined experimental and finite element research work focused on the modes of deformation, formability limits, forming forces, and resistance strength that lap joints produced with the new bi-material cylindrical inserts are able to withstand before failing. Results allowed designing a simple and easy to fabricate bi-material cylindrical insert that overcomes the main problems that have been pointed out to the metallic inserts earlier proposed by the authors.

Deformation behavior in multi-point forming using a strip steel pad

The blank is prone to wrinkles and spring-back in multi-point forming, seriously affecting the quality and forming accuracy of the formed part. To improve this state, a sandwich structure constructed from a strip steel pad and blank was presented. The deformation behaviour and forming accuracy using three forming processes, namely, without a cushion, using a polyurethane elastic pad and using a strip steel pad, were analysed by numerical simulation and experimentation. The results showed that the use of the strip steel pad in multi-point forming can effectively increase the deformation resistance of the sheet bending; make the material evenly thinned during forming; suppress defects such as wrinkles, spring-back, dimples and straight edges; and improve the forming accuracy.

Exploiting data in smart factories: real-time state estimation and model improvement in metal forming mass production

Modern production systems have numerous sensors that produce large amounts of data. This data can be exploited in many ways, from providing insight into the manufacturing process to facilitating automated decision making. These opportunities are still underexploited in the metal forming industry, due to the complexity of these processes. In this work, a probabilistic framework is proposed for simultaneous model improvement and state estimation in metal forming mass production. Recursive Bayesian estimation is used to simultaneously track the evolution of process state and to estimate the deviation between the physics-based model and the real process. A sheet bending mass production process is used to test the proposed framework. A metamodel of the process is built using proper orthogonal decomposition and radial basis function interpolation. The model is extended with a deviation model in order to account for the difference between model and real process. Particle filtering is used to track the state evolution and to estimate the deviation model parameters simultaneously. The approach is tested and analysed using a large number of simulations, based on pseudo-data obtained from a numerical sheet bending model.

Springback Calibration of a U-Shaped Electromagnetic Impulse Forming Process

A three-dimensional (3D) finite-element model (FEM), including quasi-static stamping, sequential coupling for electromagnetic forming (EMF) and springback, was established to analyze the springback calibration by electromagnetic force. Results show that the tangential stress at the sheet bending region is reduced, and even the direction of tangential stress at the bending region is changed after EMF. The springback can be significantly reduced with a higher discharge voltage. The simulation results are in good agreement with the experiment results, and the simulation method has a high accuracy in predicting the springback of quasi-static stamping and electromagnetic forming.

Solution of the problem of sheet bending by the slip line field method

One of the limitations imposed on this process of bending is the possibility of cracking on the surface of the sheet during bending. To predict this type of metal destruction, information is needed on the plastic properties of the material and the stress state in the deformation zone during the bending process. The solution of the problem of sheet bending under conditions of a flat-strained state by graphical construction of the slip line field using a rigid cylindrical mandrel has been analyzed. The material model is a perfectly plastic body. The stresses in the deformation zone and accumulated strains have been determined. The bending process is characterized as unidirectional and monotonous. It has been determined that the mean stress on the outer surface of the sheet during bending equals to 1, and it does not depend on the sheet thickness and the radius of the rigid cylindrical mandrel. Verification of the accuracy of the graphical solution is made. The resulting solution can be used as the basis for an experimental method for testing the plastic properties of metals.